Soy is one of the most nutritious foods in the world, and particularly rich in proteins. While soy’s general nutritional benefits are not in doubt, some question its impact on human hair.
Some studies have even suggested that soy actually worsens some hair conditions. Is there any truth to this? And depending on the answer, what does this mean for you? Read on to find out.
What is Soy?
Soy is a general term for products made from soybeans. The beans are seeds from Glycine max, a plant initially cultivated in China. From China, soybean cultivation spread to the rest of the world.
Some of the most popular soy products include:
- soy milk
- soy oil
The United States is the world’s leading producer of soybeans. Most of its production goes towards making soybean oil and livestock feeds.
Is Soy Good for Your Hair?
At present, the available studies do not allow us to answer this conclusively. Overall, however, most research suggests that soy is actually good for your hair.
The following are some of the main study results on this question.
Soy May Prevent Androgenic Alopecia
According to one study, soy may help to slow down or prevent the progress of Androgenic Alopecia (AGA – also called male-pattern baldness) (1). To understand why this is so, it is useful to look first at the underlying biology of AGA.
AGA is linked to a male hormone called dihydrotestosterone (DHT). This hormone is a by-product of another male hormone, testosterone (2).
Scientists do not understand the molecular mechanism by which DHT disrupts hair growth. Yet they are certain that DHT is involved because drugs that block the action of DHT typically halt hair loss. Also, people who for genetic or medical reasons have no DHT in their system, never go bald (3).
Whatever the mechanism, the end result is that DHT leads to the so-called miniaturization of hair follicles on the scalp. The hair follicles literally shrink in size with each hair growth cycle. Eventually, their hairs become so small that they no longer protrude through the scalp.
Soy May Inhibit DHT
After we eat soy, our bodies break it down into a molecule called equol. This is made from the digestion of proteins. According to research, equol behaves like a selective anti-androgen. It effectively binds and blocks the function of DHT without inhibiting testosterone (4).
This means that the growth of hair follicles proceeds uninterrupted.
The results of the above study are in line with a similar study carried out in Colorado State’s College of Veterinary Medicine.
The researchers concluded that equol, the molecule resulting from the digestion of soy proteins, can prevent the development of both prostate cancer and baldness.
They found that equol “handcuffs” DHT thereby preventing it from attacking the hair follicles. The research head, Professor Robert Handa, had this to say:
“Directly binding and inactivating DHT without influencing testosterone gives equol the ability to reduce many of the harmful effects of androgens, [male hormones] without affecting the beneficial ones.”
Although this evidence suggests soy can actually help you prevent androgenic alopecia, you should take the results with some precaution. The evidence is limited, and research into the topic is still inconclusive.
Soy May Alleviate Alopecia Areata (AA)
A different study suggests that soy extracts can alleviate alopecia areata, a scalp condition associated with inflammation of hair follicles that leads to hair loss (5).
In the study, mice were fed different amounts of soy oil – 1%, 5%, and 20% of soy oil. At the end of the study, the results revealed that the mice developed some resistance to alopecia areata induced through skin grafting.
The highest resistance was in mice that had been put on a 20% soy oil diet, suggesting that the response was largely dose-dependent. In addition, the injection of isoflavone genistein (a protein inhibitor in soy) into mice actually reduced the occurrence of AA.
Soy Added to Shampoos Makes Them More Effective
It turns out that soy-based surfactants are very effective when added to commercial shampoos.
A study published in the International Journal of Cosmetic Science evaluated the performance of soybean oil-based polymeric surfactant (SBPS) in model shampoo formulations (6).
The results showed that a shampoo formulation containing SBPS and an additional anionic surfactant (the study used sodium lauryl sulfate) exhibited better foaming and cleaning ability compared to a shampoo containing sodium lauryl sulfate as the only surfactant.
In addition, the study showed that SBPS makes it possible to reduce the concentration of sodium lauryl sulfate in commercial shampoos without compromising performance. As such, soy-based surfactants (which are actually less expensive) can help in reducing the price of hair shampoos.
Soy Can Help Keep the Scalp Hydrated
Research also suggests that the isoflavone genistein found in soy extract can stimulate the production of hyaluronic acid (HA).
This is a carbohydrate found in most parts of the body, including the dermis and the epidermis. HA is present in the scalp tissue, where it holds water and helps form a gelatinous fluid. This fluid keeps the deep tissues in the scalp nourished and hydrated.
Such an environment is perfect for the growth of hair follicles.
The Evidence on Balance
Taken together, the available research suggests that soy is a food that can actually protect from hair loss.
It is important to remember that soy is very rich in proteins and can be very good for the entire human body. If the rest of the body is healthy, this means that there will be plenty of nutrients to help your hair grow.
If you are interested in using a healthy diet to support strong hair growth, then soy is a food that could be on your short-list.
Who Should Avoid Soy?
Although soy is safe for most people, certain groups might want to avoid it altogether. These are:
- Breast cancer survivors. The effect of soy isoflavones on breast cancer survivors has been the subject of conflicting research results. Some studies concluded that isoflavones can promote the reproduction of cancerous cells. Though the research is inconclusive, some physicians advise breast cancer survivors to avoid soy and soy-based products.
- People who are allergic to soy. Soybean allergy is one of the most common allergies, especially among babies and young children (7). The Food Allergen Labeling and Consumer Protection Act (FALCPA) in the United States requires that all products containing soy must include the word “soy” on the label.
Research regarding the effects of soy on hair remains inconclusive. Most studies are leaning on the positive side, suggesting that soy can help prevent hair loss and enhance healthy hair growth.
Despite the positive evidence, it is also very important to have realistic expectations. Taking soy products may not guarantee you protection from hair loss. It is advisable to consult with your doctor when making major dietary changes.
If you are looking for a hair loss solution with more chances of success, you might have to go for a combination of proven medical treatments that are right for you.